This invention relates to an article of manufacture and methods for making the article and for determining the useful life of an article. More particularly, it relates to a determination of an article's fatigue capability.
A serious problem faced by the designer of an article is the selection of a configuration sufficient for the material of construction of the article to prevent fatigue failure under the article's intended operating conditions for a desirable period of time. Because fatigue of materials is extremely complex and fatigue failures common, it is the subject of extensive investigation at considerable expense. Yet is is commonly accepted that there is still no completely acceptable design prediction technique.
Basic material properties, such as yield strength, ultimate tensile strength, reduction in area and Young's modulus, as well as a variety of interrelationships between properties, such as that relating stress intensity to crack growth rate under selected conditions, are data generally determined during the development of the material itself. However, it has been advisable for many critical articles to determine the fatigue characteristics of a designed article by testing the article itself prior to its introduction into actual service and, in certain difficult applications, by observing the performance of the article during actual operation. This, of course, is a very time-consuming and costly method for determining the fatigue characteristics of the article.